Digital hydraulics is an emerging field in fluid power, complementing conventional hydraulic and potentially improving efficiency and dynamic performance. High speed electrically controlled on/off valves are key enablers for many digital hydraulic systems, and specifically for digital pump/motors. This work investigates a 4-quadrant 3-piston digital pump/motor utilizing two electrically controlled high speed on/off valves per displacement chamber. The test unit was simulated, built, and experimentally tested. Simulation and experimental results showed the importance of valve response times on the overall performance and efficiency of the digital pump/motor, where a small error in the delay in the valve opening or closing could lead to significant energy losses.

To minimize the impact of valve variability, a real-time valve correction algorithm was developed to account for the error in valve timing. The algorithm uses the pressure readings at the low and high pressure ports to detect the time at which the pressure ripple occurred and then obtain the delay in the valve timing. It calculates the turn-on and turn-off valve delay times in all displacement chambers in a three-piston pump with two valves per chamber, detecting a total of 12 valve delay times. The code was tested for sequential flow diverting and sequential flow limiting operating modes at a wide range of displacement (25% to 100%) with pressures ranging from 25 bar to 105 bar and shaft speeds up to 700 rpm (limited by the valves speed). It was also tested for flow diverting mode and gave good results for displacements between 70% and 100%. The error in the calculated delay times was below 5% in all of the tested conditions, providing major improvements to the digital pump system, and to digital hydraulics in general.

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